The invention relates to abrasive articles suitable for modifying a semiconductor wafer.
Chemical mechanical planarization (CMP) processes are used in semiconductor wafer fabrication to polish and planarize a semiconductor wafer. CMP processes involve placing an abrasive between a relatively stiff pad and a semiconductor wafer and moving the pad and the semiconductor wafer in relation to each other to modify the surface of the wafer. The abrasive can be in the form of a fixed abrasive element, e.g., an element that includes abrasive particles bonded to a backing, or a slurry, i.e., a liquid medium that includes abrasive particles. The support pad used in CMP processes that employ a fixed abrasive element is referred to as a subpad and includes a continuous rigid layer disposed on a resilient layer. The fixed abrasive element is often attached to the rigid layer and the resilient layer is often attached to a machine platen.
CMP processes attempt to remove material selectively from relatively higher locations, i.e., features having dimensions on the scale of those features commonly produced by photolithography, to planarize the wafer surface. CMP processes also attempt to remove material uniformly on the scale of the semiconductor wafer so that each die on the wafer is planarized to the same degree in an equivalent period of time. The rate of planarization for each die is preferably uniform over the entire wafer. It is difficult to achieve both of these objectives simultaneously because semiconductor wafers are often warped or curved. Some semiconductor wafers also include numerous step height variations or protrusions, which are produced during the fabrication sequence of an integrated circuit on a wafer. These height variations and the curvature and warp of the semiconductor wafer can interfere with the uniformity of the polishing process such that some regions of the wafer become over polished while other regions remain under polished.
In one aspect, the invention features an abrasive article that includes a fixed abrasive element, a resilient element, a rigid element disposed between the resilient element and the fixed abrasive element, and a plurality of microstructures disposed between the rigid element and the fixed abrasive element. In one embodiment, the microstructures are bonded to the rigid element. In another embodiment, the microstructures are bonded to the rigid element through an adhesive composition. In other embodiments, the microstructures extend from the rigid element.
In some embodiments, the microstructures include a layer substantially coextensive with the fixed abrasive element. In other embodiments, the plurality of microstructures is in the form of a discontinuous layer.
In one embodiment, the article further includes a microstructure element that includes a first plurality of microstructures having a first dimension and being disposed on a first region of the microstructure element, and a second plurality of microstructures having a second dimension and being disposed on a second region of the microstructure element. In one embodiment, the first region has a first microstructure spacing density, and the second region has a second microstructure spacing density.
In other embodiments, the article further includes a microstructure element that includes a first region that includes the microstructures and having a first microstructure spacing density and a second region that includes the microstructures and having a second microstructure spacing density.
In some embodiments, a cross-section of the microstructures has a shape selected from the group consisting of a polygon, a circle and an ellipse. In other embodiments, the microstructures have a shape selected from the group consisting of pyramidal, cylindrical, conical, frusto-hemispherical, frusto-pyramidal, frusto-conical and other frusta. In another embodiment, the microstructures are arranged in a pattern. In one embodiment, the microstructures are arranged in a pattern that includes offset rows of microstructures. In some embodiments, the microstructures are arranged in a pattern that includes aligned rows of microstructures.
In other embodiments, the microstructures include particles disposed in a binder. In some embodiments, the particles include polytetrafluoroethylene. In other embodiments the microstructures include a thermoplastic polymer. In another embodiment, the microstructures include a thermoset polymer. In some embodiments, the microstructures include metal, e.g., a metal selected from the group consisting of stainless steel, nickel, chromium and combinations thereof. In some embodiments, the microstructures include ceramic. In other embodiments, the microstructures further include metal and the ceramic is disposed on the metal. In still other embodiments, the microstructures include glass. In some embodiments, the microstructures further include metal and the glass is disposed on the metal.
In one embodiment, the microstructures have a height no greater than about 250 xcexcm. In one embodiment, at least about 120 microstructures/cm2 are disposed between the rigid element and the fixed abrasive element. In some embodiments, the microstructures have a cross-sectional area of no greater than about 10,000 xcexcm2. In other embodiments, the microstructures have a cross-sectional area of no greater than about 50,000 xcexcm2. In some embodiments, the microstructure element has no greater than about 20% bearing area.
In another embodiment, the abrasive element includes a first region that includes structures that includes abrasive particles and a second region free of abrasive particles. In some embodiments, the fixed abrasive element includes a textured, fixed abrasive element. In other embodiments, the article further includes a microstructure element that includes the microstructures and a backing and the microstructures are disposed on the backing. In some embodiments, the rigid element includes rigid segments. In one embodiment, the rigid segments extend from a common substrate.
In another aspect, the invention features an abrasive article that includes a fixed abrasive element that includes a backing and a composition disposed on a first major surface of the backing, the composition includes a binder and a plurality of abrasive particles, and a microstructure element bonded to a major surface of the abrasive element opposite the abrasive surface, the microstructure element including a plurality of microstructures. In some embodiments, the article further includes a rigid element and the microstructure element is bonded to the rigid element. In one embodiment, the article further includes a rigid element and the microstructures extend from the rigid element.
In other aspects, the invention features an abrasive article that includes an abrasive element that includes a plurality of structures disposed on a first surface of the abrasive element, the structures being at least essentially free of abrasive particles, and a plurality of microstructures bonded to a second surface of the abrasive element, the second surface being opposite the first surface. In some embodiments, the abrasive article further includes a rigid element and the microstructures are disposed between the rigid element and the abrasive element. In other embodiments, the abrasive article further includes a resilient element and the rigid element is disposed between the resilient element and the abrasive element.
In another aspect, the invention features an apparatus for modifying the surface of a workpiece, the apparatus that includes a fixed abrasive element, a resilient element, a rigid element disposed between the resilient element and the fixed abrasive element and a plurality of microstructures disposed between the rigid element and the fixed abrasive element. In one embodiment, the fixed abrasive element is movable relative to the plurality of microstructures. In some embodiments, the plurality of microstructures and the rigid element are movable relative to the fixed abrasive element. In other embodiments, the apparatus further includes a first web that includes the fixed abrasive element, a second web that includes the plurality of microstructures and a third web that includes the resilient element.
In some embodiments, at least one of the first web, the second web and the third web are movable relative to another of the first web, the second web and the third web. In other embodiments, the second web further includes the rigid element. In other embodiments, the microstructures extend from the rigid element. In some embodiments, the rigid element includes rigid segments. In another embodiment, the rigid segments extend from a common rigid substrate.
In other aspects, the invention features a method of modifying the surface of a semiconductor wafer that includes contacting an above-described abrasive article a substrate suitable for the manufacture of semiconductor devices, and moving the substrate and the abrasive article relative to each other. In some embodiments, the method further includes contacting a first region of the abrasive article with the substrate, the first region that includes a first plurality of microstructures having a first cross-sectional area, moving the substrate and the abrasive article relative to each other, contacting a second region of the abrasive article with the substrate, the second region that includes a second plurality of the microstructures having a second cross-sectional area, and moving the substrate and the abrasive article relative to each other. In another embodiment, the abrasive article further includes a web that includes the plurality of microstructures and the method further includes indexing the web from a first position to a second position.
The xe2x80x9capparent contact areaxe2x80x9d of a microstructure refers to the surface area of a microstructure that appears to be available for contact with an abrasive element when the two entities are in contact with each other under some applied load.
The phrase xe2x80x9c% bearing areaxe2x80x9d refers to the area on an article that constitutes the apparent contact area relative to the total planar area of the article in a given region of the article, e.g., a region of the article having a planar area similar or equal to the planar area of a semiconductor wafer.
Microstructures disposed between a relatively more rigid element and a fixed abrasive element provide points of rigid support to the fixed abrasive element. The points of rigid support facilitate substrate planarization and can reduce the amount of overpolishing that tends to occur at the edges of individual dies on the surface of the semiconductor wafer being modified with the article. An abrasive article constructed with microstructures can also provide good polishing at the submicron level.
The presence of the microstructures in the abrasive article can also alter the degree of polishing imparted by the fixed abrasive article and enhance the degree of polishing that occurs during a CMP process.
Other features of the invention will be apparent from the following description of preferred embodiments thereof, and from the claims.